Buggy code:
class CollectionGenericConverter implements GenericConverter { private GenericConversionService conversionService ; public CollectionGenericConverter ( GenericConversionService conversionService ) { } public boolean canConvert ( TypeDescriptor sourceType , TypeDescriptor targetType ) { } public Object convert ( Object source , TypeDescriptor sourceType , TypeDescriptor targetType ) { } private boolean isArrayToArray ( TypeDescriptor sourceType , TypeDescriptor targetType ) { } private Object convertArrayToArray ( Object source , TypeDescriptor sourceType , TypeDescriptor targetType ) { } private boolean isArrayToCollection ( TypeDescriptor sourceType , TypeDescriptor targetType ) { } private Object convertArrayToCollection ( Object source , TypeDescriptor sourceType , TypeDescriptor targetType ) { } private boolean isCollectionToArray ( TypeDescriptor sourceType , TypeDescriptor targetType ) { } private Object convertCollectionToArray ( Object source , TypeDescriptor sourceType , TypeDescriptor targetType ) { } private boolean isCollectionToCollection ( TypeDescriptor sourceType , TypeDescriptor targetType ) { } public Object convertCollectionToCollection ( Object source , TypeDescriptor sourceType , TypeDescriptor targetType ) { Collection sourceCollection = ( ( Collection ) ( source ) ) ; TypeDescriptor sourceElementType = sourceType . getElementTypeDescriptor ( ) ; if ( sourceElementType == ( TypeDescriptor . NULL ) ) { sourceElementType = getElementType ( sourceCollection ) ; } TypeDescriptor targetElementType = targetType . getElementTypeDescriptor ( ) ; if ( ( sourceElementType == ( TypeDescriptor . NULL ) ) || ( sourceElementType . isAssignableTo ( targetElementType ) ) ) { if ( sourceType . isAssignableTo ( targetType ) ) { <START_BUG> return source ; <END_BUG> } else { Collection targetCollection = CollectionFactory . createCollection ( targetType . getType ( ) , sourceCollection . size ( ) ) ; targetCollection . addAll ( sourceCollection ) ; return targetCollection ; } } Collection targetCollection = CollectionFactory . createCollection ( targetType . getType ( ) , sourceCollection . size ( ) ) ; GenericConverter converter = conversionService . getConverter ( sourceElementType , targetElementType ) ; for ( Object element : sourceCollection ) { targetCollection . add ( converter . convert ( element , sourceElementType , targetElementType ) ) ; } return targetCollection ; } private TypeDescriptor getElementType ( Collection collection ) { } private boolean isArrayToObject ( TypeDescriptor sourceType , TypeDescriptor targetType ) { } private Object convertArrayToObject ( Object source , TypeDescriptor sourceType , TypeDescriptor targetType ) { } private boolean isObjectToArray ( TypeDescriptor sourceType , TypeDescriptor targetType ) { } private Object convertObjectToArray ( Object source , TypeDescriptor sourceType , TypeDescriptor targetType ) { } private boolean isCollectionToObject ( TypeDescriptor sourceType , TypeDescriptor targetType ) { } private Object convertCollectionToObject ( Object source , TypeDescriptor sourceType , TypeDescriptor targetType ) { } private Object convertObjectToCollection ( Object source , TypeDescriptor sourceType , TypeDescriptor targetType ) { } }

Fix:
return sourceCollection ;